These screws attach to the hard drive and allow for secure installation Compatibility: MacBook 13" A1278 (2008), MacBook Pro 13" A1278 (2009, 2010, 2011, 2012) Compatibility: MacBook Pro 15" A1286 (2008, 2010, 2011, 2012);MacBook Pro 17" A1297 (2009, 2010, 2011)